diff --git a/Lib/test/test_memoryio.py b/Lib/test/test_memoryio.py
index 68657aa..007a092 100644
--- a/Lib/test/test_memoryio.py
+++ b/Lib/test/test_memoryio.py
@@ -638,6 +638,17 @@
         memio.close()
         self.assertRaises(ValueError, memio.__setstate__, (b"closed", 0, None))
 
+    check_sizeof = support.check_sizeof
+
+    @support.cpython_only
+    def test_sizeof(self):
+        basesize = support.calcobjsize(b'P2PP2P')
+        check = self.check_sizeof
+        self.assertEqual(object.__sizeof__(io.BytesIO()), basesize)
+        check(io.BytesIO(), basesize )
+        check(io.BytesIO(b'a'), basesize + 1 + 1 )
+        check(io.BytesIO(b'a' * 1000), basesize + 1000 + 1 )
+
 
 class CStringIOTest(PyStringIOTest):
     ioclass = io.StringIO
diff --git a/Misc/NEWS b/Misc/NEWS
index 0440114..dcba56a 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -92,6 +92,9 @@
 Library
 -------
 
+- Issue #15489: Add a __sizeof__ implementation for BytesIO objects.
+  Patch by Serhiy Storchaka.
+
 - Issue #15487: Add a __sizeof__ implementation for buffered I/O objects.
   Patch by Serhiy Storchaka.
 
diff --git a/Modules/_io/bytesio.c b/Modules/_io/bytesio.c
index 51fad21..ae8c1c1 100644
--- a/Modules/_io/bytesio.c
+++ b/Modules/_io/bytesio.c
@@ -794,6 +794,17 @@
     return 0;
 }
 
+static PyObject *
+bytesio_sizeof(bytesio *self, void *unused)
+{
+    Py_ssize_t res;
+
+    res = sizeof(bytesio);
+    if (self->buf)
+        res += self->buf_size;
+    return PyLong_FromSsize_t(res);
+}
+
 static int
 bytesio_traverse(bytesio *self, visitproc visit, void *arg)
 {
@@ -835,6 +846,7 @@
     {"truncate",   (PyCFunction)bytesio_truncate,   METH_VARARGS, truncate_doc},
     {"__getstate__",  (PyCFunction)bytesio_getstate,  METH_NOARGS, NULL},
     {"__setstate__",  (PyCFunction)bytesio_setstate,  METH_O, NULL},
+    {"__sizeof__", (PyCFunction)bytesio_sizeof,     METH_NOARGS, NULL},
     {NULL, NULL}        /* sentinel */
 };